Multi-degree-freedom electric motor

ABSTRACT

The present invention provides a multi-degree-of-freedom electric motor having a spherical rotor which is able to obtain a uniform torque and which achieves a fine and smooth rotational control. A plurality of projections consisting of magnetic material are disposed on surface of spherical rotor and a spherical stator is disposed with a predetermined space therefrom. Electromagnets are buried in the surface of the stator with predetermined intervals. The spherical rotor is caused to float in a non-contact state by gas jetted from spherical static pressure bearing via gas cylinder and pressure pipe. By the controller of the present invention, electromagnets of the stator are excited to a desired position in α/β/γ directions of orthogonal coordinates, and upon action with the projections, the spherical rotor is rotated to the position.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electric motor having a sphericalrotor which is able to rotate in a multi-degree-of-freedom.

2. Description of the Prior Art

As a prior art, there is one, for example, disclosed by the Japaneselaid-open patent application No. Hei 5(1993)-64417, construction ofwhich is shown in FIGS. 5 and 6. In FIG. 5, in an outer surface of aspherical rotor 1, which is hollow, a plurality of permanent magnets 2are buried in a lattice state so that adjacent polarities are differentfrom each other as shown in FIG. 6, and various detectors and the like40 are provided within the spherical rotor 1.

On an outer side of the spherical rotor 1, there is provided a stator 3with a certain space therefrom, and in a concave surface of the stator 3which opposes the surface of the spherical rotor 1, a plurality ofelectromagnets are buried in a lattice state.

Numeral 5 designates a bearing which supports the spherical rotor 1 in anon-contact state. The bearing 5 causes the spherical rotor 1 to floatby jetted gas supplied from a gas cylinder 6 via a pressure pipe 9.

Numeral 8 designates a controller, which functions to compute arespective size of components in a direction, β direction and γdirection in 3 axes orthogonal coordinates based on an actuation command(vector) for the spherical rotor 1, to compute a relative position ofthe permanent magnets 2 and the electromagnets based on an input of acurrent position in the α direction, β direction and γ direction from asensor (not shown) and to excite the electromagnets of the stator 3 in apredetermined pattern to actuate the spherical rotor 1 to rotate in theα direction, β direction and γ direction with a time allotmentproportional to the respective size of the components.

Also, the Japanese laid-open patent application No. Sho 59(1984)-17860discloses projecting teeth consisting of a magnetic material which areprovided in place of the above-mentioned permanent magnets. In thisprior art, torque is obtained by an attractive force betweenelectromagnets and magnetic substances and there is no need of changingan exciting direction of the electromagnets as in the above-mentionedprior art, thus the spherical rotor can be rotated only with "on-off"action of the electromagnets in accordance with a predetermined excitingpattern.

Further, as another prior art, the Japanese laid-open patent applicationNo. Hei 6(1994)-253582 discloses an electric motor having a sphericalrotor wherein projections of a magnetic substance are provided in alattice state wherein each projection is provided at each apex of aplurality of objects having triangular planes inscribing a sphericalenveloping surface of the spherical rotor.

Also, in U.S. Pat. No. 5,413,010, an electric motor in which permanentmagnets are arranged in a lattice state on a surface of a sphericalrotor is disclosed, and an art in which an electric motor having thesame kind of spherical rotor is applied to a control moment gyro isdisclosed in U.S. Pat. No. 5,476,018 and a similar example applied to anagitator is disclosed in U.S. Pat. No. 5,542,762, respectively.

In the above-mentioned prior art, there is a problem in that, as thepermanent magnets 2 and the like are arranged on the outer surface ofthe spherical rotor 1 and the pitch between the permanent magnetsbecomes inevitably narrow in the vicinity of the pole and further as thepitch between the permanent magnets in the direction of 2 orthogonalaxes and that in the oblique direction are largely different from eachother, a large variation and irregularity in the torque generated by theexcitation of the electromagnets occurs.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide amulti-degree-of-freedom electric motor which is able to obtain a uniformtorque and which is able to perform a fine and smooth rotationalcontrol.

In order to attain the afore-mentioned object, the present inventionprovides a multi-degree-of-freedom electric motor which consists of aspherical rotor having a plurality of projections consisting of amagnetic material on a spherical surface thereof, a bearing supportingthe spherical rotor rotatably and a stator disposed with a predeterminedspace from the spherical surface of the spherical rotor and having aplurality of electromagnets on a surface thereof opposing the sphericalsurface of the spherical rotor. The present invention is furthercharacterized in that each of the projections of the spherical rotor isdisposed at each triangular apex of a plurality of triangles inscribingan outer spherical surface of the spherical rotor wherein the pluralityof triangles consist of a combination of two kinds of isoscelestriangles, one being such that one side is 0.40 R and each of the othertwo sides is 0.35 R and the other being such that one side is 0.40 R andeach of the other two sides is 0.41 R, where R is a spherical radius ofthe spherical rotor.

The present invention also provides a multi-degree-of-freedom electricmotor as mentioned above, which is characterized in that each of theprojections of the spherical rotor has an enveloping surface of its tipformed spherically and a non-magnetic material is filled between each ofthe projections so as to form a same enveloping surface.

In the multi-degree-of-freedom electric motor of the present invention,the projection consisting of a magnetic material is disposed at eachtriangular apex of the plurality of triangles formed on the surface ofthe spherical rotor and a non-magnetic material is filled between eachof the projections, thus the projections are thereby disposed regularlyon the entire spherical surface of the spherical rotor and a uniformrepetitive magnetic field can be formed, so that a uniform torque can beobtained.

Accordingly, at the time when the electromagnets of the stator areexcited with a predetermined pattern to rotate the spherical rotor to adesired direction, variations of the torque can be prevented and if theprojections are disposed as many as possible, resolution is enhanced anda fine and smooth rotational control becomes possible to achieve.

In the present invention described as above, the multi-degree-of-freedomelectric motor consisting of the spherical rotor having the plurality ofprojections consisting of a magnetic material on a spherical surfacethereof, the bearing supporting the spherical rotor rotatably and thestator disposed with a predetermined space from the spherical surface ofthe spherical rotor and having the plurality of electromagnets on asurface thereof opposing the spherical surface of the spherical rotor,is characterized in that each of the projections of the spherical rotoris disposed at each triangular apex of the plurality of trianglesinscribing the outer spherical surface of the spherical rotor and theplurality of triangles consist of a combination of two kinds ofisosceles triangles. One of the triangles being such that one side is0.40 R and each of the other two sides is 0.35 R and the other trianglebeing such that one side is 0.40 R and each of the other two sides is0.41 R, where R is the spherical radius of the spherical rotor, therebythere is caused no such problem as in the prior art that the pitchbetween the permanent magnets in the direction of 2 orthogonal axes andthat in the oblique direction are largely different from each other, andthe projections being disposed uniformly on the surface of the sphericalrotor, the torque can be made uniform and a fine and smooth rotationalcontrol becomes possible.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a view of entire construction of a multi-degree-of-freedomelectric motor of one embodiment according to the present invention.

FIG. 2 is a cross sectional view of a spherical rotor of themulti-degree-of-freedom electric motor of FIG. 1.

FIG. 3 is a view of an arrangement of projections of the spherical rotorof the multi-degree-of-freedom electric motor of FIG. 1.

FIG. 4 is a block diagram showing a construction of a controller of themulti-degree-of-freedom electric motor of FIG. 1.

FIG. 5 is a view of entire construction of a multi-degree-of-freedomelectric motor in the prior art.

FIG. 6 is a view of an arrangement of projections of a spherical rotorof the multi-degree-of-freedom of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Herebelow, description is made on one embodiment according to thepresent invention with reference to figures. FIG. 1 is a view of entireconstruction of a multi-degree-of-freedom electric motor of theembodiment of the present invention, FIG. 2 is a cross sectional view ofa spherical rotor of the multi-degree-of-freedom electric motor shown inFIG. 1, and FIG. 3 is a view of an arrangement of projections of thespherical rotor of FIG. 2.

In FIG. 1, numeral 21 designates a spherical rotor, which is hollow andis provided with various detectors etc. 40 therewithin. Numeral 23designates a stator, which is partially spherical and is disposed with acertain space from a portion of the surface of the spherical rotor 21.In a side surface of the stator 23 opposing the spherical rotor 21, aplurality of electromagnets are buried with a predetermined intervalfrom each other so that the upper surfaces of these electromagnets forma spherical surface.

Numeral 25 designates a spherical static pressure bearing which causesgas supplied from a gas cylinder 26 via a pressure pipe 29 to be jettedonto the surface of the spherical rotor 21 and which causes thespherical rotor 21 to float so as to be supported rotatably and in anon-contact state. Numeral 28 designates a controller for excitingelectro-magnets provided on the surface of the stator 23 with apredetermined pattern to rotate the spherical rotor 21 (control thereofis described later concretely).

The spherical rotor 21 is provided with a plurality of projections 30 asshown in FIG. 2. That is, as clearly understood from FIG. 2, on aspherical shell 31 of a soft magnetic material, there are provided aplurality of columnar projections 30 and also provided are spacers 34 ofnon-magnetic material between the projections 30. The surfaces of theprojections 30 and the surfaces of the spacers 24 inscribe a sphericalenveloping surface and form a spherical surface.

In FIG. 3, a one eighth portion of the spherical rotor 21 is shown. Asshown there, each of the projections 30 is disposed at a position ofeach triangular apex of a combination of two kinds of isoscelestriangles inscribing an outer spherical surface of the spherical rotor21. One triangle being such that one side is 0.40 R and each of theother two sides is 0.35 R and the other triangle being such that oneside is 0.40 R and each of the other two sides is 0.41 R, where R is aspherical radius of the spherical rotor 21 and the total number of theprojections 30 amounts to 92. That is, each one projection 30 isdisposed at each apex of hexagons and pentagons which form a pattern offootball and at each center thereof.

FIG. 4 is a block diagram showing a construction of a controller 28 ofthe multi-degree-of-freedom electric motor of FIG. 1 and description ismade on a rotational control of the spherical rotor 21. Firstly, from aposition detector 47, a current position of the spherical rotor in a αdirection, β direction and γ direction of orthogonal coordinates, originof which is a center of the spherical rotor 21, is inputted into amover/stator relative position computing part 49 within the controller28. This relative position computing part 49 makes comparisons with aknown mounting position of the stator 23 to obtain a relative positionin the α direction, β direction and γ direction of the orthogonalcoordinates and outputs the obtained signals to an excitingelectromagnet selection part 42.

On the other hand, an actuation direction command δ (vector) is inputtedfrom outside of the controller 28 and this command value δ is inputtedinto the exciting electro-magnet selection part 42 and an α direction/βdirection/γ direction composite ratio computing part 41, respectively.The α direction/β direction/γ direction composite ratio computing part41 obtains a respective size of components of α direction, β directionand γ direction of the command value δ and outputs signals of αdirection, β direction and γ direction to the exciting electromagnetselection part 42 with a time allotment proportional to the respectivesize of the components.

The exciting electromagnet selection part 42 is provided withpredetermined electromagnet exciting patterns (3 patterns) for rotatingthe spherical rotor 21 to the α direction, β direction and γ directionbased on the relative position to the stator 23, as in the prior art,and an exciting pattern corresponding to the signal from the αdirection/β direction/γ direction composite ratio computing part 41 isselected first. Exciting directions (plus direction or minus directionin each direction) in the exciting pattern selected to the actuationdirection command δ are obtained next. Then, upon signals of theexciting pattern, the exciting directions and the mover/stator relativeposition computing part 49, electromagnets to make "on/off" are selectedand these selected signals are outputted to an exciting current outputpart 43.

The exciting current output part 43 outputs or interrupts an excitingcurrent for each of electromagnets 1 to n disposed on the stator 23based on the signals inputted from the exciting electromagnet selectionpart 42 so that the spherical rotor is rotated upon action with theprojections of the spherical rotor 21.

The electromagnets of the stator 23 being excited by the predeterminedpattern and the spherical rotor 21 being rotated to the desireddirections, as mentioned above, wherein the projections on the surfaceof the spherical rotor 21 are disposed uniformly on the entire sphericalsurface, uniform torque without variation can be obtained, and yet thenumber of the projections is as large as 92, thus resolution is enhancedand a fine and smooth rotational control becomes possible.

What is claimed is:
 1. A multi-degree-of-freedom electric motorcomprising:a spherical rotor comprising a plurality of projections on aspherical surface of said spherical rotor, wherein said plurality ofprojections comprise a magnetic material; a bearing supporting saidspherical rotor so as to allow said spherical rotor to be rotatable; anda stator disposed within a predetermined space from the sphericalsurface of said spherical rotor, wherein said stator comprises aplurality of electromagnets on a surface thereof which opposes thespherical surface of said spherical rotor; wherein each of saidplurality of projections of said spherical rotor is disposed at one of aplurality of triangular apexes of a plurality of triangles inscribing anouter spherical surface of said spherical rotor, wherein said pluralityof triangles comprise a combination of two kinds of isosceles triangleswherein a first one of the two kinds of isosceles triangles has a sidehaving a length of 0.40 R and has two other sides having a length of0.35 R and wherein a second one of the two kinds of isosceles triangleshas a first side having a length of 0.40 R and has two second sideshaving a length of 0.41 R, wherein R is a spherical radius of saidspherical rotor.
 2. A multi-degree-of-freedom electric motor as claimedin claim 1, further comprising a non-magnetic material disposed betweeneach of said plurality of projections of said spherical rotor, andwherein an enveloping surface is formed by tips of each of saidplurality of projections of said spherical rotor so as to form anenveloping spherical surface.